This invention relates to seismic isolation bearings for structures and machines, specifically to rubber bearings having tapered steel pin yielders.
It is common to mount structures and machines on seismic isolation bearings, sometimes referred as base isolators.
Bridges and buildings commonly use rubber bearings reinforced with steel plates. Machines mostly use steel coil springs combined with snubbers. Rubber bearings are made of high damping rubber or else are supplemented with lead or steel yielder for energy dissipation. Known metallic yielders in rubber bearings destroy vertical isolation. The viscous and hysteretic damping portion in a high damping rubber bearing is difficult to separate, yet that is a must for proper design. Steel spring mounts for machines are unable to provide energy dissipation, thus have wide bearing movements, which need to be limited by snubbers. The machine impacting on snubber may receive higher acceleration then from the ground due to seismicity. Snubbers are also used for rubber bearings. For extremely high vertical loads sliding type seismic isolators are also used. However, their friction coefficient can not be maintained constant and they have no vertical isolation and uplift capacity, all needed by design.
U.S. Pat. No. 4,644,714 discloses a friction type isolation bearing, which incorporates rigid snubber.
U.S. Pat. Nos. 4,605,106 and 4,718,206 to Fyfe et al. (1986 and 1988) disclose high damping rubber bearings. In such rubbers the velocity and the displacement related damping components are virtually inseparable, thus their seismic design is difficult.
U.S. Pat. No. 4,117,637 discloses rubber bearings with lead core yielder. The lead is a rigid body across these isolators carrying a high potion of the vertical load and preventing vertical isolation. Saw cut bearings had shown that the lead may be pumped out of its core due to its softness under repeated compression and shear loadings.
Steel is more ductile and a more reliable yielder than lead. Thus several attempt have been made to use steel yielders in rubber bearings. U.S. Pat. Nos. 4,727,695 and 5,215,382 and 5,242,147 to Kemeny (1988, 1993 and 1993, my own patents) are using steel plate or dowel yielders in rubber bearings with little effort to provide uniform volumetric yielding. Due to low cycle fatigue, their local yielding limits the number of consecutive earthquakes the bearings can balance. U.S. Pat. No. 4,910,930 to Way (1990) uses an external coil yielder which yields locally but that locality is shifting during an earthquake. U.S. Pat. No. 4,823,522 to White (1989) discloses uniform yielders but these yield one way only. Therefore are used as supplemental dampers in interstories and not in base isolators. An italian company, named FIP, offers a sliding bearing with uniform yielder, which crosses the bearing vertically. The ballhead at the end of its yielder fixes the lateral force height, which facilitate its design but limits the yielder's displacement. Also imposes unwanted tension on the yielder and result in strength degradation.
Rubber bearings require temporary ties for transportation and handling before installation. Rubber bearings are limited in volume, thus in size. That is due to maximum allowed bach volume and heat absorption capacity of the unvulcanized compound. Yet, today greater bearings are in demand increasingly.
Yielders internal to the rubber bearing are well protected from corrosion, but are uninspectable. External yielders are visually inspectable. Known bearings has either internal or external yielders. Bearings to provide for these two options within the same mechanism are unknown today.
The most frequently used bearing today in the USA contains lead in great quantity. Lead is, however, environmentally hazardous. Bearings are designed to be replaceable. After such a replacement the lead disposition remains to be a problem, thus bearing specifications favor unleaded bearings.
Rubber manufacturing takes place far from populated cities due to gases emitted in the process. Also due to hazardous solvent use. Rubber do not dissolve naturally when disposed. Therefore several rubber product is made of revulcanized, recycled rubber, such as shredded tire flakes. Such rubber helps cleaning the environment and provides jobs in populated cities due to its environmental friendly technology. Strong glues makes it possible today to utilize recycled rubber cold bonded in isolation bearings. Such bearing is much cheaper then a hot vulcanized of the same size and quality.
It is therefore the main object of this invention is to provide a seismic isolation rubber bearing with steel energy dissipators, yielding uniformly in both horizontal way, without interference with vertical isolation.
The other objects of this invention are:
a) to provide displacement limiting capability to rubber bearing utilizing its steel yielders; PA1 b) to provide uniform yielding in the bearing's steel yielders without imposing other than bending in them at any displacement; PA1 c) to provide modular bearing construction allowing to increase bearing sizes to exceed the limits imposed by current rubber technology; PA1 d) to provide elastomeric support to machines with ductile displacement limiters and energy dissipators but without local yielding of the bearing's anchoring element; PA1 e) to provide for the possibility of external and internal yielder placement in the bearing without changing bearing mechanism; PA1 f) to provide unleaded bearing saving our environment; PA1 g) to provide the possibility of using environmental friendly, recycled, cold bonded rubber as well as hot vulcanizing without the need to change bearing system or mechanism; PA1 h) to provide the possibility of bridge, building and machine base isolation without the need to change system or mechanism.